1. Field of the Invention
The invention is directed to a multiple-clutch device, such as a double-clutch device, for an arrangement thereof in a drivetrain of a motor vehicle between a drive unit and a transmission, wherein the clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission.
2. Description of the Related Art
A clutch device of this type is known, for example, from EP 0 931 951 A1. The clutch device serves to connect the drive of a motor vehicle with a multiple-speed shift transmission via two friction clutches which are preferably automatically actuated, wherein a disengagement or release system is allocated to each of these two friction clutches, so that the two friction clutches can be engaged or released independently from one another. A clutch disk of one of the two friction clutches is arranged on a central transmission input shaft so as to be fixed with respect to rotation relative to it, while a clutch disk of the other friction clutch engages at a second transmission input shaft so as to be fixed with respect to rotation relative to it, this second transmission input shaft, constructed as a hollow shaft, enclosing the central transmission input shaft. The known double-clutch is arranged with a fixed thrust plate of one friction clutch at a flywheel of an internal combustion engine. To this extent, the arrangement of the double-clutch in a drivetrain substantially corresponds to the arrangement of conventional (single-)friction clutches in the drivetrain.
Double-clutch devices (called simply double-clutches) of the type mentioned above have attracted great interest recently and are generally formed of two wet or dry clutches which are switched alternately, possibly also with overlapping. Particularly in connection with a multiple-speed shift transmission, clutches of this type make it possible to carry out shifting processes between two respective transmission speeds of the transmission without interruption of tractive forces.
In principle, double-clutch devices make it possible for both clutches to be applied jointly in especially difficult starting processes, particularly those common in car racing. For this purpose, the accelerator pedal can be deflected to its stop, as the case may be, while the motor vehicle is kept essentially stationary at the same time by applying the maximum braking force until the clutch has reached its optimal transmission point. When the braking action is canceled at the moment of reaching the optimal transmission point, the vehicle is started with maximum acceleration. Starting processes of this kind are also considered for motor vehicles with a relatively weak engine under extreme starting conditions, for example, when starting on an obstruction; that is, they are not considered only for racing cars.
Obviously, starting processes of the type described above lead to high slippage with a correspondingly extensive development of heat. This presents the problem of carrying away this heat from the area of the friction clutch serving as starting clutch. Further, a correspondingly high wear of the friction clutch must be taken into account. Moreover, heating of the friction clutches is accompanied by changes in the coefficient of friction of the friction clutches, so that control of the release mechanisms of the two friction clutches, and therefore control of the two friction clutches relative to one another, can be appreciably impaired. Since inaccuracies or changes in the functional matching of the two friction clutches relative to one another caused by heat can have the result that a torque ratio not intended in the shifting process is applied to the transmission input shafts, shifting processes in the shift transmission can be subjected to load. The synchronization in the shift transmission can be overtaxed in this way, so that, in the worst case, the shift transmission can be damaged to the point of complete failure, apart from disadvantages with respect to efficiency which occur in any case. On the whole, mismatching between the two friction clutches caused by heat is incompatible with a problem-free torque transmission in shifting processes in the shift transmission without interruption of tractive force and without jerking during shifting.
Another problem area in a double-clutch device relates to starting processes carried out in opposition to an inclination, wherein the motor vehicle must be prevented from rolling backward, or those which are used when parking at the lowest possible speed, for example, for precise positioning of a motor vehicle in a parking space. The operating states mentioned above are referred to in technical circles as xe2x80x9chill-holdingxe2x80x9d and xe2x80x9ccreepingxe2x80x9d. Both starting processes have in common that the friction clutch serving as starting clutch is operated, sometimes without actuation of the accelerator, over a longer period of time with slip. Although the torques to be transmitted in such starting processes lie well below those occurring under the operating conditions described above, especially in car racing, an intensive heating of the respective friction clutch or even both friction clutches can occur, resulting in the problems detailed above.
Suggestions have been made for gear-shifting strategies and shifting processes for double-clutch transmissions based on the aimed for adjustment of clutch slip (German reference DE 196 31 983 C1) with consequent generation of friction heat. Depending on driving behavior, overheating problems of the type mentioned above cannot be ruled out.
The risk of intensive overheating exists not only in a dry friction clutch, but can also occur in so-called xe2x80x9cwetxe2x80x9d friction clutches, possibly in the form of a disk or plate clutch, which are operated by the action of a viscous operating medium such as hydraulic fluid. By way of example, a gear change box with two plate clutches is known from German reference DE 198 00 490 A1, wherein one plate clutch is provided for forward driving and the other for driving in reverse. German reference DE 198 00 490 A1 is concerned primarily with providing adequate cooling of the two plate clutches using the viscous operating medium. In spite of the liquid cooling, heating of the friction clutches is also a considerable problem in plate clutches because the operating medium, which usually flows through friction facing grooves or the like to carry off the heat, cannot be guided through between the plates in optional quantity. The reason for this is that, on one hand, excessive flow through the friction facing grooves or the like would build up a counterpressure between the friction surfaces of two adjacent plates and would therefore reduce the capacity of the friction clutches to transmit torque (with a corresponding increase in slip and therefore additional generation of friction heat, so that the problem of overheating is exacerbated) and, on the other hand, the operating medium could be overheated and destroyed when flowing through between the plates. Overheating in plate clutches can result in that the friction surfaces can no longer separate from one another completely during a disengaging process and, consequently, torques can still be transmitted via the clutch which should be disengaged, so that considerable drag torques can reach the associated shift transmission. When plates clutches are used in a multiple-clutch device, especially a double-clutch device, of the type mentioned above, shifting processes could again be brought under load in the shift transmission with resulting overtaxing of the synchronization in the shift transmission.
One approach to mastering overheating problems in the area of friction clutches in case of unfavorable operating conditions, for example, with problematic starting processes in a motor vehicle, is to provide another starting element in addition to the first and second clutch arrangements which is in the form of a hydraulic clutch or hydrodynamic clutch and comprises a hydrodynamic circuit with an impeller wheel, a turbine wheel and, if desired, a stator wheel. The driving member can be connected in parallel with one of the two friction clutches; that is, it can act on a common transmission input shaft irrespective of the engagement state of this friction clutch. A clutch device in which two plate clutches and a starting element of this type are integrated, was described in the German Patent Application 199 46 857.5 by the present Applicants which was applied for on Sep. 30, 1999 and whose disclosure is incorporated in the subject matter disclosed in the present application.
Within the framework of investigations undertaken by the present Applicants in connection with double-clutch devices, it was shown in general that wet-type clutches exhibit sealing problems and problems relating to output losses. Further, it was shown that boundary conditions relating to the available axial and radial installation space could be adhered to only with difficulty, if at all, based on the previously known concepts. With regard to clutches, possibly, diaphragm clutches, which are actuated by pistons integrated in the clutch device, the arrangement of the piston chambers associated with the pistons proved especially problematic.
It is the object of the present invention to achieve improvements with respect to at least one of the problems mentioned above and/or other problems.
With respect to the problems under discussion relating to the occurrence of friction heat in clutch devices, it is suggested according to a (first) aspect of the invention for a multiple-clutch device, possibly a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, which clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, that at least one of the clutch arrangements, preferably at least one clutch arrangement which has a greater effective friction radius and which possibly serves as a starting clutch, is constructed as a plate clutch arrangement. In this connection, it is further suggested that plates in a plate stack of the plate clutch arrangement which have at least one friction facing can be brought into frictional engagement with plates having no friction facing, wherein at least one of the plates not having a friction facing is thicker in axial direction than friction facing carrying elements of adjacent plates having at least one friction facing. This suggestion is based on the insight that at least some of the plates can be used as xe2x80x9cheat buffersxe2x80x9d which temporarily store friction heat occurring in many operating situations to an excessive degree with respect to the possibilities for dissipating heat, such as by means of a cooling fluid that may be provided, and which carry off the heat only at a later time when there is no friction heat or only a little friction heat in this plate clutch arrangement. Overheating states of the clutch arrangement which can lead to the problems discussed above can then be prevented or their consequences can at least be controlled. It is advantageous for a high heat storage capacity when the plates which are thicker in axial direction are produced from a material with a high heat capacity, for example, steel.
In close relation to this aspect of the invention it is suggested, according to another (second) aspect of the invention, for a multiple-clutch device, such as a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, which clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, that at least one of the clutch arrangements, preferably at least one clutch arrangement which has a greater effective friction radius and which possibly serves as a starting clutch, is constructed as a plate clutch arrangement, and that at least one plate which has at least one friction facing of sintered material and at least one plate which has at least one friction facing made of another friction facing material are provided in a plate stack of the plate clutch arrangement, wherein the other friction facing material has a progressive frictional coefficient curve in relation to a slip speed. The step according to the second aspect is preferably taken in combination with the step according to the first aspect.
The idea behind the step according to the second aspect is that friction facings of sintered material conduct heat appreciably better than friction facings of other materials. Therefore, with the use of friction facings of sintered material, it is also possible to make available the friction facing carrying elements carrying the sintered material facings as xe2x80x9cheat buffersxe2x80x9d within the meaning explained above. It would be expected for this reason that it would be optimal to produce all friction facings from sintered material. However, it has been shown that such a construction of the plate clutch arrangement promotes unwanted torsional vibrations in the drivetrain. This is because a friction facing of sintered material exhibits a degressive frictional coefficient curve over the slip speed, that is, a frictional coefficient which decreases at higher slip speed (dxcexc/dxcex94N less than 0). Therefore, according to the invention, the plate stack has at least one friction facing made from a different friction facing material which has a progressive curve of the coefficient of friction in relation to slip speed at which the coefficient of friction accordingly increases as the slip speed increases (dxcexc/dxcex94N greater than 0). The curve of the coefficient of friction of the plate stack with respect to a slip speed is preferably adjusted on the whole so as to be progressive or at least approximately neutral in order to prevent self-excitation of torsional vibrations in the drivetrain and/or to damp torsional vibrations in the drivetrain.
Regarding the respective friction facing carrying element which carries the at least one friction facing of sintered material, it is suggested for purposes of the highest possible xe2x80x9cheat storage capacityxe2x80x9d that this friction facing carrying element is produced from a material with a high heat capacity, possibly from steel, and/or that this friction facing carrying element is thicker in axial direction than a friction facing carrying element carrying at least one friction facing of the other friction facing material. The other friction facing material can be a paper material, for example, which has proven successful in clutch construction generally and has a relatively sharp progressive curve of the coefficient of friction.
With respect to providing the greatest possible heat buffer (a heat capacity which is as large as possible), it is suggested according to a third aspect of the invention for a multiple-clutch device, such as a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, which clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, that at least one of the clutch arrangements, preferably at least one clutch arrangement which has a greater effective friction radius and which possibly serves as a starting clutch, is constructed as a plate clutch arrangement, wherein one of the clutch arrangements which is constructed as a plate clutch arrangement and which preferably has the larger effective friction radius is in a torque transmission connection with an input side, e.g., a clutch device hub, of the clutch device or with an output side of the plate clutch arrangement via a torque transmission member, and wherein the torque transmission member has a friction surface against which the plate stack of the plate clutch arrangement can be pressed in the course of an engagement of the clutch arrangement.
As a rule, the torque transmission member has a substantially larger mass than an individual plate and can accordingly provide a large heat capacity. The torque transmission member is therefore particularly well-suited for temporary storage of friction heat which could occur in excessive amount in many operating situations with respect to the heat dissipation possibilities before this heat is carried off at a later time. Accordingly, by itself or in combination with the steps according to the first and second aspects of the invention, overheating states of the clutch arrangement can be prevented or their consequences can at least be controlled.
The torque transmission member can be coupled with the input side and a plate carrier, such as an outer plate carrier, of the plate clutch arrangement so as to be fixed with respect to rotation relative to it. It can be a metal plate, e.g., a sheet metal plate, which resembles a wall, if desired, and which has a metal surface portion or sheet metal surface portion serving as friction surface. It is also possible to provide the torque transmission member with a friction facing. In this case, with respect to providing the heat capacity of the torque transmission member for heat storage, a friction facing material having good heat conductivity should be used, for example, the sintered material mentioned above. In this case, a sintered material surface portion serves as friction surface.
With respect to an axially and radially compact construction of the clutch device, it may be required to construct the torque transmission member so as to be curved in cross section and to provide only a radially shorter friction surface as friction surfaces of the plate stack. This can lead to problems when the plate which can be brought into frictional engagement with the friction surface is a plate having a facing, for example, a paper plate, and projects radially over the friction surface of the torque transmission member. Due to uneven area pressure (the plate is generally too thick and consequently not sufficiently flexible to ensure a uniform area pressure), so-called facing splitting can result. In order to remedy this, it is suggested that, when it is a plate having a friction facing, the respective plate of the plate stack which can be brought into frictional engagement with the friction surface (this plate can be called the end plate) has a different average friction radius than other plates of the plate stack which have friction facings. The end plate can be an outer plate, for example, and can extend less far radially inward than other outer plates of the plate stack; that is, it can extend as far inward radially as is sensible with respect to the radial dimensioning of the friction surface of the torque transmission member with respect to a uniform area pressure. The rest of the plates of the plate stack of the same type, that is, for example, the rest of the outer plates, can have a larger radial dimensioning, since the plate which follows the end plate in the plate stack and which does not have a friction surface can distribute the pressing forces between the plates to a larger radial area and can also provide for a larger radial area for a uniform area pressure.
According to a fourth aspect of the invention, for a multiple-clutch device, such as a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, which clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, it is suggested that the first clutch arrangement and the second clutch arrangement are constructed as plate clutch arrangements, wherein one of the two plate clutch arrangements has a larger number of plates than the other. The purpose of this suggestion is to increase the total available heat capacity for one plate clutch arrangement in that more plates are provided which can serve as xe2x80x9cheat buffersxe2x80x9d.
The one plate clutch arrangement preferably has an appreciably larger effective friction radius than the other plate clutch arrangement because the plates having the larger effective friction radius therefore have a larger mass than a plate having a smaller effective friction radius (assuming comparable dimensioning in radial direction, i.e., a comparable distance from the outer radius to the inner radius, of the plates).
Since both steps, namely, the increase in the number of plates and the greater effective friction radius in relation to a reference input quantity, for example, a reference actuation pressure, lead to a greater torque transmission capacity (for example, a greater maximum torque that can be transmitted), it is particularly advisable to use a plate clutch arrangement as starting clutch. Because of the resulting reduced area pressure at the friction surfaces, the wear occurring in slip states during starting is reduced.
In a preferred further development, steps are taken so that the torque transmission capacities of the two plate clutch arrangements at least approximate one another with respect to a reference input quantity, possibly a reference actuation pressure, which determines the strength of the frictional engagement of the plates and which is the same for both clutch arrangements. In this way, it is achieved that both clutch arrangements have at least approximately the same torque-transmitting capacity based on the same input quantity, that is, they can transmit the same torque at this same input quantity (for example, the maximum hydraulic pressure that can be delivered by a hydraulic pressure shaft). Consequently, in the case of a hydraulic actuation of the plate clutch arrangements for purposes of engagement, the two clutch arrangements can be controlled on the basis of an identical relationship between the transmitted or transmissible torque and the hydraulic pressure, and, for example, a common pressure regulator or the like can be used in connection with a simple switching valve for both plate clutch arrangements.
Each of the clutch arrangements can have an actuating piston defining a pressure chamber for actuation, preferably for engagement, of the clutch arrangement by means of a pressure medium, preferably hydraulic medium. In order to adapt the torque-transmitting capacities of the clutch arrangements to one another, it is suggested in this connection that the actuating piston of the plate clutch arrangement with the smaller effective friction radius and/or with the smaller number of plates have/has a pressure application surface exposed to the pressure medium at least for actuating the clutch arrangement which is larger than the actuating piston of the plate clutch arrangement, the plate clutch arrangement with the larger effective friction radius and/or with the greater number of plates.
According to a fifth aspect of the invention for a multiple-clutch device, such as a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, which clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, it is suggested that at least one of the clutch arrangements, preferably at least one clutch arrangement which has a greater effective friction radius and which possibly serves as a starting clutch, is constructed as a plate clutch arrangement and has a plate stack in which plates that are located opposite one another can be brought into mutual frictional engagement at respective pairs of friction surfaces for engagement of the clutch arrangement. With a view to making the area pressure in the plate stack more uniform and/or to prevent facing splits and the like, a plurality of friction surface pairs are provided in the plate stack which differ appreciably from one another with respect to their effective friction radius. For example, friction facings which extend radially from an inner radius to an outer radius and differ appreciably with respect to their inner radius and/or outer radius can be provided in the plate stack. It is possible, for example, that outer plates which extend radially from an inner radius to an outer radius and which have different inner radii are provided in the plate stack. Further, it is possible, for example, that inner plates which extend radially from an inner radius to an outer radius and which have different outer radii are provided in the plate stack.
In order to render the area pressure more uniform, it can be extremely advantageous when plates having no friction facing are provided in the plate stack, wherein the plates have a radial outer radial area and a radial inner radial area and at least one of the plates, preferably a plurality of plates, can be or are brought into frictional engagement with friction facings of adjacent plates on both sides only in the radial outer radial area and/or at least one of the plates, preferably a plurality of plates, can be or are brought into frictional engagement with friction facings of adjacent plates on both sides only in the radial inner radial area and/or at least one of the plates, preferably a plurality of plates, can be or are brought into frictional engagement with friction facings of adjacent plates on both sides in the radial inner radial area as well as in the radial outer radial area. For this purpose, at least one friction facing can be allocated to an adjacent plate in the plate stack and positioned radially with respect to it in such a way that a friction facing area pressure is rendered uniform and/or a temperature profile opposing a deformation of the plate leading to uneven friction facing area pressure can be adjusted in the adjacent plate using friction heat.
This reason for this step is that uneven cooling of the plates not having friction facings, for example, steel plates, regularly occurs along their radial height, which can result in deformations (so-called sagging) of the plates with the risk that this could lead to an uneven area pressure in the plate stack. This involves the risk of facing splits due to uneven pressure. By providing for a deliberate heating of a plate having no friction facing in a determined radial area, the deformation of the plate can be influenced in order to prevent an unwanted deformation of the plate or to mitigate this deformation or to compensate for a deformation, unwanted per se, of another plate with respect to rendering the area pressure more uniform. For example, the plates having no friction facings could alternately be brought into frictional engagement and consequently heated locally only in a radial outer radial area and only in a radial inner radial area along the axial extension of the plate stack. However, it is often also sufficient when only one plate or a few plates are brought into frictional engagement and heated only on the radial inner side or only on the radial outer side, since the area of the plate that is not heated opposes a deformation of the plate due to internal forces which act in the plate and which are based on the resulting temperature profile.
In this connection, it is generally advisable that at least one plate in the plate stack can be brought into frictional engagement with a neighboring plate in a first radial area and with a neighboring plate in a second radial area which clearly differs from the first radial area. The first radial area can extend farther radially outward than the second radial area. Further, the second radial area can extend farther radially inward than the first radial area. The plate stack can have friction facings made of paper material and/or friction facings made of sintered material. Friction facings made of sintered material are advantageous insofar as this material exhibits comparatively good heat conduction, as was stated above, so that the respective plate carrier can serve as a heat buffer and, to this extent, opposes overheating of the plates with consequent excessive deformation.
The features of a multiple-clutch and a drivetrain which were indicated in connection with the different aspects of the invention can be advantageously combined. Further independent aspects of the invention will be discerned by the person skilled in the art from the preceding explanations and the description of the Figures.
The invention is further directed to a drivetrain for a motor vehicle with a clutch device, according to at least one aspect of the invention, arranged between a drive unit and a transmission.
The invention will be described more fully in the following with reference to embodiment examples shown in the Figures.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.